1. Field of the Invention
Embodiments of this invention relate generally to seals for fluid-tight compartments for use at depth, and in particular embodiments, to seals that prevent the ingress of fluid into the compartment, yet allow pressurized fluid such as gas to escape from within the compartment.
2. Description of Related Art
Compartments are often used to protect items from the effects of humidity, moisture, and fluids generally. Openings to such compartments must therefore be sealed in a fluid-tight manner. However, the use of a fluid-tight seal may also prevent the escape of pressurized fluid that has built up inside the compartment. It is therefore desirable to have a seal that prevents the ingress of fluids, yet allows pressurized fluids to escape from within the compartment.
An example of a fluid-tight compartment with a need for pressurized fluid venting is the battery compartment of submersible flashlights. Batteries give off hydrogen gas during their operation. In most flashlights, the interior compartment is not airtight, so hydrogen gas given off by the batteries escapes into the environment and does not accumulate in the battery compartment. However, flashlights designed for use in humid or wet conditions or even underwater must provide a fluid-tight interior compartment to prevent corrosion and electrical shorts in circuitry within the compartment. The sealing mechanisms used to make the interior compartment of the flashlight fluid-tight also prevent fluids such as gas from escaping the compartment. Hydrogen gas emitted from batteries will therefore accumulate within the compartment, and may explode if a spark occurs when an operator switches the flashlight on or off.
It is therefore desirable to absorb the hydrogen gas emitted from the batteries or allow it to escape the interior compartment of the flashlight, yet maintain a fluid-tight seal. Hydrogen absorbing pellets have been placed within the interior compartment of waterproof flashlights to absorb hydrogen gas and eliminate the hazard. However, flashlights with multiple or powerful batteries, leaking or defective batteries, reversed polarity batteries, or a combination of old and new batteries may give off more hydrogen gas than the pellets can absorb. In addition, the pellets may become damaged or saturated with moisture, reducing their effectiveness.
To supplement the gas-absorbing pellets, gaskets that act as one-way valves have been used on gaps and orifices of fluid-tight flashlights. These gaskets, typically formed as a lip seal having a flexible flange inclined away from the flashlight interior, prevent fluids from entering the flashlight interior through the gaps or orifices, yet allow hydrogen gas and other fluids under sufficient pressure within the flashlight interior to escape. One such gap exists between the head and body of fluid-tight flashlights that actuate by rotating the head of the flashlight with respect to the body. To maintain a fluid-tight seal, a gasket must be located between the rotating head and body around the entire circumference of the flashlight and must maintain compressive force against the head and body sufficient to prevent the ingress of fluids at all times, even during rotation of the head with respect to the body. The compressive force is also needed to provide frictional resistance during rotation of the head with respect to the body to prevent accidental activation of the flashlight or disengagement of the head from the body. An example of such a gasket is disclosed in U.S. Pat. No. 5,207,502 (see, e.g., FIG. 14, element 49), incorporated herein by reference.
Gaskets that act as one-way valves must allow trapped fluids to overcome the compressive force of the gasket in order for it to escape, and thus the compressive force of the gasket against the head and body of the flashlight must be limited. Gaskets shaped as flexible flanges inclined away from the flashlight interior provide this limited compressive force and one-way valve effect. However, by limiting the compressive force of the gasket, the sealing ability of the gasket is reduced around the entire circumference of the flashlight, increasing the chance of fluid breaching the gasket and reaching the interior compartment. This problem is compounded when a poor fit exists between the head and body due to severe impact, warpage, or dimensional tolerances in the manufacturing of the head and body. In addition, the limited compressive force of the gasket against the head and body of the flashlight reduces the frictional resistance encountered when the head of the flashlight is rotated with respect to the body, increasing the chance of accidental activation of the flashlight or disengagement of the head from the body.
Therefore, there is a need for a fluid pressure relief seal that maintains high compressive forces between the cover and body of a compartment to prevent the ingress of fluid into the compartment, yet allows pressurized fluid within the compartment to escape. In particular, such a fluid pressure relief seal is needed between the rotating head and body of submersible flashlights, where it can maintain high compressive forces on the head and body to prevent the ingress of fluid, yet allow pressurized gas within the flashlight to escape. The high compressive forces are also desirable to maintain high frictional resistance when rotating the head of the flashlight with respect to the body to decrease the chance of accidental activation of the flashlight or disengagement of the head from the body. In accomplishing these functions, it is desirable to keep the fluid sealing mechanism separate from the fluid venting mechanism to allow high compressive forces to be used for the sealing function without impairing the fluid venting function.